Heretofore, a balata cover has been used as the cover of the golf ball. However, an ionomer having excellent durability and cut resistance has recently been used as the base resin of the cover because the balata cover is inferior in durability and cut resistance. This ionomer cover is used not only as the cover of the solid golf ball but also the cover of the thread wound golf ball. The ionomer cover is exclusively used in the golf ball for ordinary golfers.
Further, an ionomer having high rigidity and high hardness is used for this ionomer cover for the purpose of increasing the flying distance by enhancing resilience performances.
However, the golf ball wherein the above ionomer having high rigidity and high hardness is used as the base resin of the cover, although exhibiting a large flying distance, has the following serious disadvantages the improvement thereof being desired.
(1) The feeling at the time of hitting is hard and the hit feeling is inferior because of the cover having high rigidity and high hardness.
(2) Since the cover has high rigidity and high hardness, sliding arises on the club face surface when hit with an iron club (hereinafter "iron shot"), the spin amount varies greatly, the flying distance is unstable, and the control properties are inferior.
In order to improve the above problems, a two-piece solid golf ball using a flexible resin having low rigidity as the cover has recently been marketed.
The golf ball using the above flexible cover material has solved the instability of the iron shot and hard hit feeling due to the cover. An extremely hard core is, however, required to be used in order to make up for deterioration in resilience performances caused by softening of the cover, and a new disadvantage is thus caused. That is, an excessive amount of spin is put on the golf ball, which results in serious deterioration in flying distance and, further, the impact force is increased and, therefore, the hit feeling becomes hard.
Therefore, there has been proposed a golf ball wherein the deterioration of flying distance caused by the softening of the cover is solved by constructing the cover with two layers; an inner layer cover and an outer layer cover composed of a soft resin and a rigid resin, respectively (Japanese Laid-Open Patent Publication No. 62-275480).
However, regarding the above golf ball, the rigid resin is used for the outer layer cover and, therefore, the hit feeling is hard and inferior. Further, slipping occurs on the face surface for the iron shot and the golf ball therefore lacks stability upon hitting.
As described above, a golf ball having performances which satisfies flying distance, stability of iron shot and hit feeling simultaneously has never been obtained, heretofore.